Frequency determining means



@(Zfi. 15, 1935. R, DOWNEY FREQUENCY DETERMINING MEANS Filed March 24,1934 Fig.1.

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1 IIMIIMA Inventor:

uw m w m m m Lmmm M K MW i H win R UlTED STATES PATENT OFFICE FREQUENCYDETERMINING MEANS Reginald L. Downey, Scotia, N. Y., assignor'to GeneralElectric Company, a corporation of New York Application March 24, 1934,Serial No. 717,224

Claims.

My invention relates to frequency determining means and it has for oneofits objects to provide an extremely economical means for measuringradio frequencies with a desired radio range.

5 A further object of my invention is to provide such means involving aminimum number of tubes and which may be incorporated in a minimum ofspace thereby to increase its applicability to use on aircraft.

A further object of my invention is to provide such means capable ofgreater stability of operation and greater accuracy than has beenpossible 'in the past and whereby the oscillation generators involvedare protected against variations in the circuits of the system otherthan those of the particular oscillation generator.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organization and method of operation,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the accompanying drawing in which Fig. 1 represents an embodimentof my invention and Fig. 2 represents a modification thereof.

Referring to the drawing, I have shown therein a frequency determiningdevice in accordance with my invention, and which employs a plurality ofelectron discharge devices I, 2, and 3. Discharge devices I and 2 are ofthe multi-grid type and operate both as oscillation generators and asamplifiers while the discharge device 3 is a threeelement electrondischarge device which serves as an audio amplifier.

All of these discharge devices are arranged to be energized from asuitable source of energy 4 the positive terminal of which is connectedthrough resistance 5 to the anode of discharge device l throughresistance 1 and inductance 8, which is shunted by a resistance 9, tothe anode of discharge device 2, and through the primary winding of anaudio transformer I!) to the anode of discharge device 3. This source ofpotential 4 also supplies operating potential to screen grids I and I2in discharge devices I and 2 through the resistances I3 and Mrespectively. The cathodes of all of the discharge devices are connectedto the negative side of the source of potential through bias resistancesl5, l6 and I1, respectively, each of these resistances being shunted bya suitable radio frequency bypass capacitor l 8. The heating elementsfor the cathodes of each of the discharge devices are also energizedfrom a portion of the source of potential 4, the circuit for theseheating elements extending through contacts on jacks l9 and 20 connectedto the secondary winding of the transformer ID. A plug 2|, to which isconnected a pair of headphones 22, 5 cooperates with the jacks l9 and 20and when inserted therein closes contacts 23 and 24 thereby energizingthe heating elements of all of the tubes through an energizing circuitincluding a portion of source 4. 10

The discharge device lhas its two grids nearest to the cathode connectedto operate as a piezo electric oscillation generator, the grid 25nearest the cathode being connected to the cathode through resistance 26and the grid bias resistance 15 I5, and the grid 21 next removed fromthe cathode being connected to the positive terminal of the source ofanode potential 4 through a fixed tuning inductance 2'? and a voltagedropping resistance 28. 20

The resistance 26 is arranged to be shunted by any one of a plurality ofpiezo electric crystals 29 dependent upon the position of a movablecontact 3D. The tuning inductance 21 has a fixed natural period outsideof the frequency range 25 of the crystals 29 so that by moving thecontact 30 into engagement with an electrode of any of the cells of thecrystals 29 a frequency determined by the particular crystal isproduced. The frequencies preferably are spaced apart in the de- 30sired frequency range and differ from each other by approximately I0kilocycles or more.

Discharge device 2 is likewise adapted by means of its two grids 36 and31 nearest the cathode to produce oscillations. These oscillations aregen- 35 erated in a circuit comprising a variable condenser 3| andeither of two inductances 32 and 33 dependent upon the position ofswitches 34 and 35, this circuit being connected between the two innergrids 36 and 31 of the discharge device 2. The 4.0 respective midpointsof the inductances 32 and 33 are connected through a resistance 38 tothe positive side of the source of anode potential whereby high positivepotential is supplied to the grid 31. The inner grid 36 is isolated fromthis source 45 of unidirectional potential by grid condenser 39 and isconnected to the negative side of the source of potential through a gridleak resistance 40. Thus these grids 36 and 3'! are connected in amanner conventional to the grid and anode of 50 three element electrondischarge devices arranged to produce oscillations.

The oscillations the frequency of which is to be determined are receivedin a receiving circuit, not shown, which may be a simple antenna, con-55 nected to the grid 4| of discharge device through a couplingcondenser 42. This grid receives its bias voltage from resistance |5 towhich it is connected through a radio frequency impedance 43 which maybe a resistance or choke coil. The anode of the discharge device I isconnected to a grid 44 in discharge device 2 corresponding to the grid4| of discharge device I. These grids 4| and 44 are spaced nearer theanode of the respective discharge devices than the oscillating grids ofthe corresponding devices and are shielded both from the anode and fromthe oscillating grids by means of the shield grids 45 and 46respectively. The anode of the discharge device 2 connected through theradio frequency impedance comprising the combination of choke coil 8 andresistance 9, and coupling condenser 41 to the grid of audio frequencyamplifier 3.

The operation of my device may now be explained.

Let us assume that the device is used, for example, to check thefrequency of an associated transmitter, as, for example, in an aircraftinstallation. The oscillations from the associated transmitter arereceived through condenser 42. Let us assume that the associatedtransmitter should produce a frequency corresponding to the naturalfrequency of one of the crystals 29. The contact 30 is placed upon therespective crystal and the plug 2| is inserted into one of the jacks I9or 20. Oscillations having the frequency of the piezo electric crystalare then produced by the crystal and supplied to the output circuit ofthe discharge device I. Similarly oscillations from the associatedtransmitter received through condenser 42 and amplified in dischargedevice I are supplied to the output circuit, both of these oscillationsbeing supplied to the grid 44 of discharge device 2 through condenser49. The discharge device 2 acts as a grid leak detector of theseoscillations whereby if the frequency of the associated transmitter bedifferent from that of the corresponding crystal 29 a beat note isproduced in the output circuit of discharge device 2, which is amplifiedin discharge device 3 and heard in the headphones 22. By means of thetuning device of the associated transmitter the operator may adjust thefrequency thereof, by listening to the headphones 22, to produce a zerobeat with the known fixed frequency produced by discharge device I undercontrol of the respective crystal 29.

Now let us assume that it is desirable to produce a frequency by theassociated transmitter which differs from that produced by any of thecrystals 29. Contact 30 is moved to engage the electrode of the crystalhaving a natural frequency nearest the frequency to be produced by theassociated transmitter. Switches 34 and 35 are then operated to theposition to connect in circuit the appropriate inductance 32 or 33 andthe condenser 3| is adjusted to cause the discharge device 2 to producea frequency equal to the frequency of the piezo electric crystal thenincluded in circuit. This adjustment may be effected by the zero beatmethod, the operator listening to the headphones 22 and adjusting thecondenser 3| until the zero beat position is found. The operator maythen refer to his chart showing the dial position frequencycharacteristic of the oscillator 2 and note any variation between thedial setting of condenser 3| and that denoted by his dialposition-frequency characteristic corresponding to the frequency of thepiezo-electric crystal. He then adjusts the condenser 3| to produce thefrequency which it is desired to produce by the associated transmittertaking into consideration the correction thus observed. He is then inreadiness to adjust the frequency of the associated transmitter which hemay do simply by adjusting the tuning device on the associatedtransmitter While listening to the headphones 22 until a zero beatposition is found between the oscillations produced by the transmitterand those produced in the circuit 32, 33.

During this latter operation the contact 30 may be moved off from any ofthe crystal cells thereby to avoid the production in the system ofoscillations of the frequency of any of the crystals. This operation,however, is not necessary Where the frequency produced by thepiezo-electric crystal differs from that for which the condenser 3| isadjusted by an amount so great that no beat notes are produced whichinterfere with the detection of the zero beat position between theassociated transmitter and the oscillations of the circuit 3|, 32, 33.

In this way the associated transmitter may be adjusted to any frequencywithin the desired range and its frequency checked with the accuracydetermined by the piezo-electric crystal.

While in the above description I have mentioned the discharge device 2as acting as the detector of oscillations received from the dischargedevice I, it will be understood that with the connections shown thedischarge device I 1 may likewise operate as a detector producing a beatnote between the oscillations produced by the crystal and those receivedthrough condenser 42. Since a capacitance resistance coupling isemployed between the anode of discharge device In accordance with myinvention either of the discharge devices and 2 may be employed as asource of oscillations to be used for purposes other than those hereinpreviously indicated. This is indicated by the fact that the anode ofdischarge device 2 is arranged to be connected through an outputcondenser 48 to any suitable high frequency utilization circuit. In theevent that it is desired to produce a frequency corresponding to thenatural frequency of one of the crystals 29 the switches 34 and 35 maybe moved to their intermediate position where no oscillations areproduced in the circuit 3|, 32, 33 or condenser 3| may be moved to aposition when the frequency produced is not objectionable in the output.responding crystal are thus supplied to the grid 44 of discharge device2 in which they are amplified and supplied through the couplingcondenser 48 to the desired utilization circuit. If the frequency to beproduced be one which differs from that produced by the piezo-electriccrystal the contact 30 may be moved off from any crystal cell and thecondenser 3| adjusted to the desired frequency switches 34 and 35 ofcourse being in one of their two alternative positions. Of course theaccuracy of this frequency adjustment may be determined by the zero beatmethod utilizing the crystals 29 and headphones 22 as previouslydescribed.

The two jacks I9 and 20 are provided for pur- Oscillations generated bythe corpose of adjusting the intensity of oscillations received in theheadphones 22. If the plug 2| be inserted in the jack ii! the headphonesare connected across the entire secondary winding of transformer Iii,whereas if it be inserted in the jack 2i] the headphones are connectedacross only a portion of this secondary winding. In this way theimpedance of the output is matched with that of the particularheadphones employed thereby to produce a maximum transfer of energy tothe headphones.

It will be observed that the circuits of both of the oscillationgenerators are shielded by grids and 36 from each other and from othercomponents of the circuit. These shield grids extend on both sides ofthe respective control grids 4| and 44. In this way improved frequencystability is obtained, the frequency of neither generator being affectedby the condition of the other generator, or by the condition of theexternal circuits such as the input circuit connected to condenser 42,or the output circuit connected to condenser 48. Thus impedancevariations and undesired radio-frequency pickup in these elements of thesystem do not effect the frequency of oscillations produced.

It frequently occurs in producing a beat note between the crystalcontrolled oscillations and oscillations produced by tube 2 that it isdesired to use a harmonic of a crystal frequency. These harmoniccurrents are weak as generated in the crystal oscillator. It has beenfound that in my system such harmonics are amplified in tube l to anenergy level comparable with the oscillations produced by tube 2 wherebythese harmonic oscillations may be utilized for the production of beatnotes quite as efficiently as the natural frequencies of the crystals.

In Fig. 2 I have illustrated a modification of my invention whichdiffers from Fig. 1 only in that grids 3t and 31 of tube 2 are connecteddifferently to produce oscillations. In this figure grid 3i is connectedto ground through condenser 50 and is operated at ground radio frequencypotential. This grid is supplied with positive operating potential frombattery 4 through resistance 38 as indicated. The cathode is connectedto ground through switch 34, left portion of one or the other ofinductances 32' and 33' and bias resistance l6 whereby it is biasedabove ground potential. Grid 36 is biased negatively with respect to thecathode by means of grid leak till and grid condenser 39 as in Fig. l.The tuned circuit of the oscillator comprises the Variable condenser 3|and either of inductances 32 and 33' which may be selectively connectedin circuit by operation of switches 34' and 35' either to the right orleft.

It will now be understood from the description given that my system iscapable of widely varying application both for the measurement andproduction of radio frequencies. It essentially incorporates but twodischarge devices, the discharge device 3 being merely an amplifierwhich may be omitted if desired. The device is especially well adaptedfor use on aircraft for determination of the frequencies of thetransmitters so employed since in its physical construction it isextremely light and may occupy a minimum of space.

While I have shown a particular embodiment of my invention it will ofcourse be understood that I do not wish to be limited thereto sincediiferent modifications both in the circuit arrangement andinstrumentalities employed may be made and I contemplate by the appendedclaims to cover any such modifications as fall within the true spiritand scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination, a pair of electron discharge devices, each of saiddischarge devices having circuit means connected therewith to generateoscillations, piezo electric means to control the fre- 10 quency ofoscillations generated by one of said means, the oscillations generatedby the other means being variable over a range including the frequencyof said piezo electric means, means whereby a beat note betweenoscillations gener- 15 ated in said two circuit means is produced in theanode circuit of one of said discharge devices, and means in saiddischarge devices to prevent variation of frequency of oscillationsgenerated by either of said circuit means from being affected by thecondition of the other circuit means.

2. In combination, a pair of electron discharge devices, each of saiddischarge devices having circuit means connected therewith to generateoscillations, piezo electric means to control the fre quency ofoscillations generated by one of said means, the oscillations generatedby the other means being variable over a range including the frequencyof said piezo electric means, a radio frequency anode circuit for one ofsaid discharge devices, a radio frequency coupling between said devicesand means in said discharge devices to shield both of said circuit meansfrom the other circuit means and from said radio frequency anodecircuit.

3. In combination, a pair of electron discharge devices, each of saiddevices having an anode, a cathode and a plurality of grids, oscillationgenerating means including a pair of grids in each device, saidoscillation generating means including the grids of one devicecomprising a piezo electric crystal, and the oscillation generatingmeans including the grids of the other discharge device comprising meansto vary the frequency of oscillations produced over a range includingthe frequency produced by said crystal, means to supply radio frequencyoscillations to an additional grid in one of said devices, a couplingbetween the anode of said one device and an additional grid in the otherdevice, and an audio frequency output circuit connected to the anode ofsaid other device whereby oscillations either generated by, or receivedin, said one'discharge device are supplied to the other discharge deviceand a beat note between said oscillations and oscillations produced insaid other device appears in said output circuit.

4. In combination, a pair of electron discharge devices, each of saiddevices having an anode, a cathode and at least three grids, meansincluding two of said grids nearest the cathode of each device toproduce oscillations therein, said means including said grids of onedevice including a piezo electric device for controlling the frequencyof oscillations produced, and said means including said grids of saidother device comprising means for adjusting the frequency over a rangeincluding a frequency controlled by said piezo electric crystal, areceiving circuit connected to a grid of said first device more remotefrom the cathode than said two grids, a coupling between the anode ofsaid first device and a grid of said second device more remote from thecathode than said two grids, and an audio output circuit connected tothe anode of said first device, whereby oscillations received in saidreceiving circuit are amplified in said first device and supplied tosaid second device, and a beat note may be produced between saidoscillations and oscillations produced by either of said means, saidbeat note appearing in said output circuit.

5. In combination, a pair of multigrid discharge devices, meansindividual to each discharge device utilizing the two grids nearest thecathode of the respective discharge device to produce oscillations, aradio frequency input connected to a grid in one of said devices moreremote from the respective cathode than said two grids, a couplingbetween the anode of said one device and a. grid of the other devicemore remote from the respective cathode than said two grids, an outputcircuit connected to the anode of said other device, and shielding meansin each device whereby said more remote grids are shielded from saidfirst mentioned two grids in the respective discharge device and fromthe respective anode.

REGINALD L. DOWNEY.

